1. Field of the Invention
This invention relates to the field of controlling the intensity of waves in inhomogeneous media, with particular but not exclusive application to the case of sound waves used to guide materials in porous media and other inhomogeneous media.
This application continues to refer to the suite of applications and the several embodiments of this invention in the field of guidance and control of the flow of materials in porous media under the generic term Acoustic Shepherding.
2. Background of the Art
Chemotherapeutic agents are injected into the body with the intent of treating disease. For example, biologically active materials may be injected into the body with the goal of killing or deactivating cells within a tumor mass. Such materials can also be injected or infused in solution into the brain to treat cancer. A problem arises since the infusate may not flow efficiently along an internal body path that leads directly to the targeted mass. Moreover, the target itself may finally be reached after an unacceptably prolonged period because of natural delays in passive diffusion or uncontrolled flow of body fluids. These delays are particularly important in the long term, since endogenous bulk flow is likely to be a significant method of transmission of molecules and even cells in the presence of injury such as edema from tumors, trauma, or hemorrhagic stroke. Such edema cause significant opening of the extracellular spaces along the tracts of white matter such as the corpus callosum, optical fiber tracts, and so on and these provide flow paths for the introduced therapeutic particles that are only temporarily open. Another disadvantage of direct infusion is that, short of chemical intervention (with undesired and potentially dangerous side effects), the characteristic distance over which the pressure and the velocity are not negligible is dependent on the distribution of blood vessels and on the permeability to hydrophilic plasma proteins which are outside the control of the infusion system parameters, thus leaving only the flow rate or the pressure of the infusion alone to drive the fluid. Of course, these driving factors too have a very limited range over which they may be varied, since too low a flow rate means that the distribution of the therapeutic molecule will be dominated by diffusion and loss, resulting in poor spread; while too high a flow rate might mean disruption to brain processes and architecture, and loss of infusate through white matter or CSF pathways.
Ultrasound methods have been used both for imaging and therapy. Most pertinent to this invention have been reports on the enhancement of drug penetration into the brain when catheterization procedures introducing drug into the blood vessels have also included ultrasound irradiation at diagnostic or higher levels: increased penetration of the drug into the brain has been noted. Such studies have been focused on opening the blood brain barrier.
In other art, the phenomenon known as acoustic streaming has been known for more than a century, following the pioneering treatment of Lord Rayleigh. Acoustic streaming is due to dissipation of acoustic wave energy and momentum in a medium, and the induced fluid velocity depends on the mechanism of dissipation. In a medium such as the brain, with compressible compartments, extracellular fluid with narrow channels, and so on, it is expected that a variety of mechanisms will contribute to the overall streaming. As a simple illustrative example, consider a streaming velocity V in the direction of propagation of an acoustic signal. In magnitude, it has the form V=AαI/μc where A is a number that depends on details of the boundary conditions and geometries of the problem, α is the attenuation coefficient of the acoustic intensity at the frequency in question, I is the intensity of the sound wave at the point in question, μ is the viscosity of the fluid, and c is the velocity of sound. The attenuation coefficient α is frequency dependent, often increasing linearly or quadratically with frequency, depending on the pertinent attenuation mechanism.
If a number of mechanisms contribute to the overall dissipation of energy, each of these mechanisms will contribute to a streaming velocity. Thus the actual magnitudes and directions of streaming velocity in the brain calls for an appropriate protocol, such as hand-in-hand development of experimental test and theoretical setup of the equations of fluid flow in a porous medium subject to acoustic irradiation, that can be solved only via computer analysis of the acoustic equations.
To summarize, while direct injection into brain parenchyma is being used, and usefully bypassing the blood-brain barrier to penetration of drugs intended to act in the Central Nervous System (CNS), the resulting drug distribution is difficult to control. Ultrasound has been tested for affecting the permeability of the blood brain barrier, and acoustic streaming has been known in the theory of porous media studied by civil engineers and those skilled in like arts. Time reversal and related techniques based on the reciprocity of the Green function in equations describing wave propagation have been proposed and developed, especially by Mathias Fink et al., for medical applications related to destroying select targets within tissue and especially brain tissue. The following paragraph gives further references to the background art.
The explanation, apparatus enablement, and background on ultrasound (acoustic) enhancement of mass flow, of reversible opening of the blood brain barrier, of time reversal techniques, ultrasound emission and the like are described for example in “Acoustic Enhancement of Diffusion in a Porous Material,” Haydock, David and Yeomans, J. M., Ultrasonics, 41, (2003) 531-538; “The Mechanism of Generation of Acoustic Streaming,” Mitome, Hideto, Electronics and Communications in Japan, Part 3, Vol. 81, No. 10, 1998; “Non-Invasive, Transcranial and Localized Opening of the Blood-Brain Barrier using Focused Ultrasound in Mice,” Ultrasound in Med. & Biol., Choi, James J. et al., Vol. 33, No. 1, pp. 95-104, 2007; “Time-Reversal Acoustics in Biomedical Engineering,” Fink, Matthias, et al., Annu. Rev. Biomed. Eng., 2003, Vol. 5, pp. 465-497; “Spatio-Temporal Coding in Complex media for Optimum Beamforming: The Iterative Time-Reversal Approach,” Montaldo, Gabriel, et al., IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 52, No. 2, February 2005; “Experimental Demonstration of Non-Invasive Transskull Adaptive Focusing Based on Prior Computed Tomography Scans,” Aubrey, J. F. et al., J. Acoust. Soc. Am., 113, (1), January 2003; “Adaptive Focusing for Transcranial Ultrasound Imaging Using Dual Arrays,” Vigno, F. et al., J. Acoust. Soc. Am., 120, (5), November 2006; “High Power Transcranial Beam Steering for Ultrasonic Brain Therapy,” Pernot, M. et al., Phys. Med. Biol., 48 (2003) 2577-2589; “Prediction of the Skull Overheating During High Intensity Focused Ultrasound Transcranial Brain Therapy,” Pernot, M. et al., 2004 IEEE Ultrasonics Symposium, pages 1005-1011; “Time Reversal of Ultrasonic Fields—Part I: Basic Principles,” Fink, Mathias, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 5, September 1992; “Time Reversal of Ultrasonic Fields—Part III: Theory of the Closed Time-Reversal Circuit,” Cassereau, Didier and Fink, Mathias, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 5, September 1992; “Time Reversal of Ultrasonic Fields—Part III: Theory of the Closed Time-Reversal Circuit,” Cassereau, Didier and Fink, Mathias, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 39, No. 5, September 1992; “Optimal adaptive focusing through heterogeneous media with the minimally invasive inverse filter,” Vignon, Francois and de Rosny, Julien and Aubry, Jean-Francois and Fink, Mathias, Journal of the Acoustical Society of America, Vol. 122, No. 5, November 2007, pages 2715-2724; “Spatial and temporal concentrating of energy in ultrasound systems by single transmitter using time-reversal principles,” Sarvazyan, A. and Sutin, A., Proceedings of World Congress on Ultrasonics, Paris, pp. 863-866, Sep. 7-10, 2003: See also further material by Dr. Sarvazyan and his colleagues at the web site of Artann laboratories www.artannlabs.com; “Patterns of Thermal Deposition in the Skull During Transcranial Focused Ultrasound Surgery,” Connor, C. W. and Hynynen, K., IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 51, No. 10, October 2004; and Published U.S. Patent Application 2004/0267234. “Brain Arterioles show more active vesicular transport of blood-borne tracer molecules than capillaries and venules after focused ultrasound-evoked opening of the blood-brain barrier”, Sheikov, Nickolai and McDannold, Nathan and Jolesz, Ferenc and Zhang, Yong-Zhi and Tam, Karen, and Hynynen, Kullervo, Ultrasound in Medicine and Biology, vol. 32, pp 1399-1409 (2006). “Local and Reversible blood-brain barrier disruption by non-invasive focused ultrasound at frequencies suitable for trans-skull sonications”, Hynynen, Kullervo and McDannold, Nathan and Sheikov, Nickolai and Jolesz, Ferenc and Vikhodtseva, Natalia NeuroImage, vol. 24, pp 12-20 (2005). Hynynen, Kullervo and McDannold, Nathan and Vikhodtseva, Natalia and Jolesz, Ferenc, Radiology, vol. 220, pp 640-646 (2001). “Spatio-temporal analysis of molecular delivery through the blood-brain barrier using focused ultrasound”, Choi, J. J. and Pernot, M. and Brown, T. R. and Small, S. A. and Konofagou, E. E., Physics in Medicine and Biology, vol. 52, pp 5509-5530 (2007). “Piezo-electric materials for high frequency medical applications: a review”, Shung, K. K. and Cannata, J. M. and Zhou, Q. F., Journal of Electroceramics, vol. 19, pp 139-145 (2007). “Unified Green's function retrieval by cross-correlation: connection with energy principles”, Snieder, Roel and Wapenaar, Kees and Wegler, Ulrich, Physical Review E vol. 75 036103-1-14 (2007). These references are incorporated herein in their entireties to provide technical information in support of the present disclosure and claims. Another prominent worker in the field of time reversal acoustics is Armen Sarvazyan and his team at Artann laboratories.
U.S. Pat. No. 5,752,515 (Ferenc A. Jolesz and Kullervo Hynynen) discloses a method and apparatus for directly applying ultrasound for the purposes of opening up the blood-brain barrier (sonoporation) and confirming the opening by the injection of a contrast agent observable with radiological imaging that is visible when the blood brain barrier is compromised. This, and other patents with Kullervo Hynynen as inventor, allow for the transducer to be placed adjacent to brain tissue, by the process of drilling a bore hole through the skull, to obviate the highly distorting effects of the skull.
U.S. Pat. No. 5,092,336 (Mathias Fink) discloses how to localize a reflective target within tissue by the application of ultrasound transmission from transceivers placed distally from the desired target, and subsequent application of time-reversal technology to process the signals reflected from the target, so that an ultrasound beam may be formed for the purposes of focusing the energy on the reflective target.
U.S. Pat. No. 5,428,999 (Mathias Fink) discloses further methods and processing schemes within the rubric of time reversal methods to localize reflective targets in tissue for the purposes of focusing ultrasound on these targets for therapeutic purposes.
U.S. Pat. No. 7,101,337 I(Jean-Francois Aubry, Mathias A. Fink, Mickael Tanter, and Jean-Louis Thomas) discloses a method for imaging, for example, brain tissue allowing for the dissipative heterogeneous acoustic properties of the skull, wherein the transceivers are outside the skull, acoustically coupled to it, and methods of signal processing are introduced to correct for the distortions produced by the skull so that the acoustic signals may propagate through the tissue and be received and decoded for imaging purposes.
U.S. Patent Application Publication 2004/0267234 “Implantable Ultrasound systems and methods for enhancing localized delivery of therapeutic systems” (Gill Heart and Axel Tolkowsky and Joe Brisken) discloses the application of intraparenchymal delivery of a therapeutic agent in solution, with an ultrasound transmitter inserted through a burr hole in the skull to the surface of the brain, coaxial with a catheter that is pumping the therapy-containing solution. The transmitted ultrasound then induces a further spread of the agent, beyond what would be obtainable from the pressure-driven infusion of the solution alone.
U.S. Patent Application Publication 2005/00277824 “Non-invasive method of obtaining a pre-determined acoustic wave field in an essentially uniform medium which is concealed by a bone barrier, imaging method and device for carrying out said methods” (Jean-Francois Aubry and Mathias Fink and Mickael Tanter) teaches a method for obtaining a desired sound field within the brain by means of echographic signal processing methods applied to signals transmitted and received by transceiver arrays positioned outside the skull.
U.S. Patent Application Publication 2006/0241529 “Adaptive Ultrasound Delivery System” (Kullervo Hynynen and Nathan McDannold) discloses a phased array of transceivers, the frequencies and positioning of which are adjusted till the desired opening of the blood brain barrier is achieved, as detected by contrast agent imaging.
All references cited are incorporated herein by reference in their entirety to support the technical nature of the disclosure, as well as those applications and publications from which priority is claimed in the section Related Applications Data.